The present invention relates generally to pressure activated switches, and more particularly, to a sensing mat having pressure activated switches contained therein for optimum surface area activation.
Various types of electrical switch mats are known in the art. Electrical switch mats have been designed for use in many different applications including use in floor mats for security, safety or other purposes to detect movement of objects or pedestrian traffic thereover. For example, it is known in the art to provide sensing mats or switch mats as part of a safety system to protect persons from injury from dangerous machinery and industrial equipment. Examples of such safety systems utilize switch mats connected to a machine controller for terminating power to the machine if someone steps on or off the mat.
Generally, electrical switch mats include one or more pressure-actuated switches incorporated within a floor mat material which protects the switch against wear. For example, normally open and normally closed pressure-sensitive electrical ribbon switches have been incorporated into numerous designs for electrical switch mats. Open and closed pressure-sensitive ribbon switches generally include a pair of either spaced or closed conductors respectively supported in an insulative jacket. Generally, relatively light pressure on the jacket will close the space in an open switch and open the conductors in a close switch thereby activating the switch. Thus, someone stepping on or off an electrical switch mat having a ribbon switch incorporated therein will activate the switch.
Electrical switch mats as described above have been extremely useful in detecting and responding to the presence, or absence, of the operator or others anywhere on its sensing surface, wherein the sensing surface is defined as the area covered by a single mat or a plurality of mats in combination. In one typical application, one or more sensing mats are placed directly in front of a piece of machinery, wherein the machine operator stands on the mat during operation of the machinery. If the operator steps off the mat, or if someone else steps on the mat, the switch mat is activated to terminate power to the machine. In another application, the dangerous equipment may be surrounded by a plurality of switch mats to define a danger zone, wherein a person entering the danger zone will step on a mat, thereby activating a switch to terminate power to the equipment.
Many of the pressure-actuated electrical switch mats presently in use generally include a major planar pressure-sensitive surface defining an active area. Pressure applied to the mat at this active area, for example by pedestrian traffic or movement of objects thereover, activates the switching device contained in the mat. However, mats of this type also typically include a perimetrical boundary or edge which is not sensitive to pressure. This “pressure-inactive” edge, while relatively small in comparison to the active pressure-sensitive surface, still provides an area which, when subjected to pressure, will not activate the switching device contained within the mat. The expanse of the inactive area is multiplied where several mats are used in juxtaposition in situations where it is desired to increase the sensing area. In particular, by abutting the inactive edges of the mats adjacent one another, the inactive area may be wide enough so that certain pedestrian traffic or movement of objects may not be detected. This results in the mats not producing the desired effect, i.e., the detection of movement of objects or people thereacross.
This problem was addressed in commonly owned U.S. Pat. No. 5,510,586 to Hacking, wherein a pressure-sensitive electrical switching device is disclosed for providing pressure-sensitive continuity between a pair of pressure-sensitive electrical switch mats, where each mat includes a major planar active area and an inactive edge. The switching device is positioned between a pair of pressure-sensitive electrical switch mats along abutting inactive edges thereof so that the area of pressure inactivity defined by the edges of the mats is eliminated.
U.S. Pat. No. 5,602,428 to Schultz et al. also proposed a switching device in the form of a bridge connector interposed between two adjacent switch mats to eliminate the inactive edge zone of each mat. The bridge connector spans over the inactive zone of each mat and connects the active zones so that pressure applied to the bridge connector will activate one or both of the adjacent mats.
The switch mat disclosed in commonly owned U.S. Pat. No. 6,054,658 to Duhon et al. does away with additional splicing or interconnecting switching devices, while at the same time maintaining an active edge zone on the mat. This is achieved by providing a rigid frame construction to the mat for supporting a ribbon switch at the perimeter edge of a top plate member of the mat. Thus, a switch mat is provided which has an activation surface encompassing the entire surface area of the mat.
It would be desirable to further improve upon the switch mat disclosed in the above U.S. Pat. No. 6,054,658 to Duhon et al. In particular, it would be desirable to provide a fully flexible, water resistant switch mat that is simply constructed and has activation across its entire surface.